This invention relates to a system and method of providing an adaptive feedrate control in NC (numerical control) machine, such as end milling, using a solid modeling based simulation of the machining process.
End mills are widely used to machine complicated parts in the aerospace and mold/die industries, yet it is somewhat difficult to achieve high productivity in end milling. Machining intricate details on parts often calls for slender cutters of low rigidity, and the cutting forces in contouring can easily exceed the limit of the cutter. For instance, the resultant force can increase by more than a factor of ten in a simple cornering cut; such a critical region causes excessive tool deflection and tool breakage. The variation in cutting force is due to the variation of metal removal rate. Frequently the geometry of the part prevents constant radial and axial depths of cut. Consequently, feed per teeth recommended assuming a constant depth of cut does not perform satisfactorily and must be adjusted. Finding out the problem areas and applying proper feedrates, if done by the part progammer, is labor intensive. Sometimes a conservative feedrate override is applied to prevent tool breakage at the expense of under-utilizing the machine capability and reducing productivity.
Up to the present, hardware adaptive controllers have been devised to improve the productivity for limited operations; one has a force sensor to measure cutting force. The controller and sensors have to be installed on the NC machine tool. Such hardware is inflexible in handling diferent situations of tooling, material and set-up, because it does not have the ability to interface with CAD/CAM systems and to configure itself for different operations. In addition, systems operating in real time cannot look ahead.
Recently, a solid modeling system which can simulate end milling in real time has been developed and is called NCS. With the NC program as an input, it continuously models the in-process workpiece geometry as a solid. This is described in the inventor's Ph.D. Thesis, "Solid Geometric Modeling for Mold Design and Manufacturing", Cornell Univ., 1984 (TIS Report No. 84CRD122, May 1984, General Electric Co. is the same); and in the published paper authored with K. K. Wang, "Geometric Modeling for Swept Volume of Moving Solids", IEEE CG&A, December 1986, pp. 8-17, the disclosure of which is incorporated herein by reference.